Monochromator

ABSTRACT

A compact monochromator with entrance and exit slits nearly incident permitting insertion and removal of the monochromator at a focal point without requiring change in the system. A monochromator with entrance and exit slits each formed by an edge and a mirror. A monochromator with entrance slit and mirror directing the beam through an aperture in a grating to a collimating mirror, defining a light path from the entrance slit and mirror to the collimating mirror to the grating and back to the collimating mirror to the exit mirror and slit.

8-2l-73 XR 397539618 united States Patent [191 Haley H51 Aug. 21, 1973MONOCHROMATOR [75] Inventor: Floyd C. Haley, La Canada, Calif.

[73] Assignee: Ultra-Violet Products, Inc.,

San Gabriel, Calif.

22 Filed: Feb. 10, 1972 211 Appl. No.: 225,248

[52] US. Cl 356/100, 350/162 R, 350/271 [51] Int. Cl G0lj 3/18, G01j3/04[58] Field of Search 350/271, 162 R; 356/74, 99-101 [56] ReferencesCited UNITED STATES PATENTS 3,594,084 7/1971 Turner 356/100 3,567,3223/1971 Brehm et a1. 356/100 X 3,451,744 6/1969 de Mey 350/271 2,995,9738/1961 Barnes et a1. 356/99 OTHER PUBLICATIONS Codling et al., Journalof Physics E: Scientific Instruments Vol. 3, September 1970, pages685-689.

Primary ExaminerRonald L. Wibert Assistant Examiner-F. L. Evans [57]ABSTRACT A compact monochromator with entrance and exit slits nearlyincident permitting insertion and removal of the monochromator at afocal point without requiring change in the system. A monochromator withentrance and exit slits each formed by an edge and a mirror. Amonochromator with entrance slit and mirror directing the beam throughan aperture in a grating to a collimating mirror, defining a light pathfrom the entrance slit and mirror to the collimating mirror to thegrating and back to the collimating mirror to the exit mirror and slit.

8 Claims, 9 Drawing Figures Patented Aug. 21, 1973 3,753,618

2 Sheets-Sheet 1 Patented Aug. 21, 1973 2 Sheets-Sheet 1 MoNocnaoMAronThis invention relates to monochromators, that is, an optical instrumenthaving a specular or broad band light beam as an input and providing anarrow band or specific wavelength beam as an output. The monochromatorusually has an adjustment or control which permits varying thewavelength of the exiting beam. A number of monochromators have beenutilized in the past incorporating various combinations of slits,gratings, prisms and mirrors. In a typical monochromator, the incomingbeam is directed through an entrance slit to a grating or a prism. Thegrating reflects the various wavelengths of the beam at difierent anglesand the prism refracts the various wavelengths at different angles. Anarrow band of this spread out beam is selected by the exit slit fortransmission onward. More complex monochromators may utilize an entranceslit, a grating, an intermediate slit, a prism and an exit slit toprovide higher selectivity.

The conventional monochromators are relatively large and require complexmechanisms and are expensive. It is an object of the present inventionto provide a new and improved monochromator which is considerablysmaller than the conventional devices and which is simpler in design andless expensive to manufacture and install. A particular object of theinvention is to provide a new and improved monochromator wherein theentrance and exit slits are nearly incident thereby permitting insertionand removal of the monochromator from an instrument without requiringany change in instrument set-up. A further object is to provide such aninstrument with nearly incident entrance and exit slits wherein the slitwidth control can be withdrawn to a position such that the incoming beammay exit without any interference from the monochromator, withoutrequiring removal of the monochromator.

The invention contemplates a monochromator with entrance an exit slitseach formed by an edge and a mirror, with the entrance slit mirrordirecting the incoming beam through an apertured grating to acollimating mirror for reflection to the grating. The beam from thegrating is reflected by the collimating mirror back through the apertureof the grating to the exit slit mirror, completing the beam path throughthe monochromator.

Other objects, advantages, features and results will more fully appearin the course of the following description. The drawings merely show andthe description merely describes the preferred embodiments of thepresent invention which are given by way of illustration or example.

In the drawings:

FIG. I is a longitudinal sectional view of a monochro matorincorporating the invention;

FIG. 2 is a sectional view taken along the line 22 of FIG. ll;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1;

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 1;

FIG. 5 is an enlarged partial sectional view taken along the line ofFIG. 3;

FIG. 6. is a view similar to that of FIG. 1 of a monochromatorincorporating an alternative and presently preferred embodiment of theinvention;

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 6;

FIG. 6 is a partial side view taken along the line 8-8 of FIG. 7; and

FIG. 9 is an end view taken along the line 9-9 of FIG. 8.

Referring to the monochromator in FIGS. 1-5, the housing includes acylindrical shell 20 with an end plate 21 attached by screws 22 andanother end plate 23 attached by screws 24. A concave mirror 25 iscarried on a plate 26 having a socket riding on a ball 27 of a screw 28.The screw 28 may be rotated in the plate 21 to advance the mirror 25within the housing. Adjusting screws 29 are mounted in the plate 21 andengage the mirror plate 26 for adjusting the angle of the mirror 25within the housing.

A pyramid 32 is formed on the plate 23 with an opening 33 defined byedges 34, 35.

A bar 40 is mounted on the plate 23 with brackets 41 and screws 42. Abeam entrance opening 44 is provided in one of the brackets 41 and abeam exit opening 45 is provided in the other bracket. A slit mirrorcarrier 46 rides on guide pins 47 and is moved toward and away from theedges 34, 35 by a manually rotatable shaft 48 threadedly mounted in theplate 40. Springs 49 are carried on the plate 40 and engage the carrier46 urging the carrier away from the edges 34, 35.

Slit mirrors 54, 55 are carried on the end of the carrier 46, themirrors typically being reflecting surfaces of a prism. The includedangle between the mirrors is slightly greater than 90, typically 91,with the apex of the prism forming the two mirrors normally beingpositioned between the edges 34, 35, as seen in FIGS. 1 and 5.

A grating 60 is mounted in a frame 61 which is supported on pivot pins62 threaded into the shell 20. A hole 63 is provided through the gratingand the frame.

Rings 65, 66 are threadedly mounted on the exterior of the shell 20. Arod 67 is fixed in the frame 61 and projects through a slot 68 of theshell into the space between the rings 65, 66. A tension spring 69 isconnected between a pin 70 in the shell and the rod 67, urging the rodinto engagement with the ring 65. The angular position of the grating isadjusted by moving the ring 65 on the shell 20, with the ring 66 servingas a locking ring.

The edge 34 and the mirror 54 define the entrance slit. Similarly, theedge 35 and the mirror 55 define the exit slit. The width of the slitsis controlled by moving the carrier 46 in and out. In operation, a beamenters through opening 44 and passes through the entrance slit. The beamis reflected by the mirror 54 through the aperture in the grating to thecollimating mirror 25 which reflects a collimated beam to the grating. Aportion of the light reflected by the grating is collected by the mirror25 and focused at the exit slit through the grating opening and themirror 55. The narrow band beam leaving the exit slit passes out throughthe opening 45. A nonreflective spot 72 or alternatively, an opening, isprovided on the reflecting surface of the mirror 25 at the center toprevent direct reflection from the slit mirrors back to the slitmirrors.

The monochromator of FIGS. 1-5 is compact and may be made quite small.Units presently being manufactured are about 3% inches outside diameterand about 6 inches overall length. The slit width is typically in theorder of 1 mm. and the entrance and exit slit edges 34, 35 are veryclose, being only a few millimeters apart and less than half acentimeter apart. With the nearly incident entrance and exit slits, themonochromater may be inserted into and removed from an optical systemwithout requiring any changes in the optical system, with the entranceand exit slits being at a focal point in the optical system. Also, themirrors 54, 55 may be moved away from the slit edges (to the right inFIG. 1) removing the mirrors entirely from the entering and exiting beampaths so that the monochromator action can be omitted and obtained asdesired in the operation of the overall system.

An alternative embodiment of the monochromator is illustrated in FIGS.6-9.. The housing is formed of a cylindrical shell 84) with an end plate81 and an end plate 82. A concave mirror 83 is carried on the end plate81 with a stud 84 and nut 85. The head of the stud 84 pro vides thenonreflecting spot at the center of the mirror 83. A bar 87 is mountedon the shell 80 over the end plate 82 by screws 88. The inner section 89of the bar 87 projects through an opening in the end plate 82. Anentrance opening 90 is provided in one side of the bar 87 and an exitopening 911 is provided in the opposite side. Another opening 92 isprovided in the inner end 89 of the bar, with the entrance edge 94between the openings 90, 92 and with the exit edge 95 between theopenings 91, 92. A prism 97 with reflecting surfaces providing theentrance slit mirror and exit slit mirror is supported on a carrier 98.A shaft 101 rotates in a bushing 102 mounted in the bar 87, with thethreaded inner end of the shaft Mill engaging a threaded opening in thecarrier 98 for moving the carrier in the bar 87. A spring 103 ispositioned between the bushing 102 and carrier 98 for eliminating playin the drive. A knob 104 is mounted on the shaft 101 for manualadjustment of the slit widths.

A grating 110 is carried in a frame llll which is pivotally mounted inthe shell 80 on studs 1112. In this embodiment the grating Jill) isshown as two pieces with a central space 114 therebetween providing thecenteral aperture for light passage between the slits and thecollimating mirror. An opening M is provided in the frame 111 for lightpassage. The gratings in both embodiments may be held in place withcement or by clips (not shown) or by other suitable means.

A mechanism is provided for adjusting the angular position of thegrating. A rod 120 is positioned in a passage 121 in the shell 80, withone end of the rod engaging the grating frame 1 1 ii and with the otherend of the rod engaging a shaft 1122 of a micrometer type adjustmentdevice 123. A knob 1124 rotates on a boss 125 mounted on the end plate811, with rotation of the knob serving to advance and retract the shaft122. Another rod 128 is positioned in a passage 129 in the shell 80,with one end of the rod engaging the grating frame 1 l1 and with theother end engaging a spring 130 positioned in the passage 1129.

In operation, the spring urges the rod 128 against the grating framethereby urging the grating frame against the rod 120 and this rodagainst the shaft 122.

The operation of the monochromator of FIGS. 6-9 is the same as theoperation of the monochromator of FIGS. 1-5. It is preferred that theinterior of the shell 80 be non-reflective and one mechanism forreducing reflection is to leave the interior of the shell 80 roughturned, as indicated by the serrations in FIGS. 6 and 7 The interior mayalso be coated with nonreflective material.

While being compact as described above the monochromator also providessuperior performance. One model of the instrument has an f number of1.12 and with a grating blazed at 2400A, has a dispersion of A per mm atthe exit slit.

1 claim:

1. In a monochromator for selecting a narrow band from an incoming lightbeam, the combination of:

a housing;

a concave mirror mounted in said housing;

slit means mounted in said housing defining entrance and exit slits; and

a grating mounted in said housing between said slit means and saidconcave mirror, said grating having an aperture for light passagebetween said slits and concave mirror;

said slit means including spaced first and second edges and first andsecond slit mirrors, with said first edge and slit mirror defining saidentrance slit and with said second edge and slit mirror defining saidexit slit, and

means for positioning said first slit mirror for reflecting an incomingbeam from said entrance slit to said concave mirror through said gratingaperture, with said concave mirror reflecting the beam from said firstslit mirror as a collimated beam to said grating and reflecting a returncollimated beam from said grating to said second slit mirror throughsaid grating aperture, and

means for positioning said second slit mirror for reflecting the beamfrom said concave mirror through said exit slit, with said concavemirror including means defining a nonreflecting zone at the centerthereof for preventing direct reflection from said entrance slit to saidconcave mirror and back to said exit slit.

2. A monochromator as defined in claim 1 including:

a frame for holding said grating;

pivot means for mounting said frame in said housing for pivoting aboutan axis parallel to said slits; and drive means carried by said housingfor moving said grating on said axis.

3. A monochromator as defined in claim 2 wherein said drive meansincludes:

mating threaded nut and shaft mounted on said housing, with rotation ofsaid nut moving said shaft;

a first rod sliding in a first passage in said housing with one end ofsaid rod engageable with said frame and with the other end engageablewith said shaft;

a second rod sliding in a second passage in said housing with one end ofsaid rod engageable with said frame; and

a spring in said second passage and urging said second rod intoengagement with said frame urging said frame into engagement with saidfirst rod urging said first rod into engagement with said shaft.

4. A monochromator as defined in claim 2 wherein said drive meansincludes:

first and second rings threadedly mounted on said housing, with saidrings engageable with each other for locking on said housing anddefining a zone between said rings;

a shaft carried on said frame and projecting into said zone; and

a spring carried on said housing and coupled to said said first andsecond edges are parallel and said first and second mirrors are mountedin a wedge form with the apex of said wedge positionable between saidedges defining said first and second slits, with the beam path to saidentrance slit in line with the beam path from said exit slit.

8. A monochromator as defined in claim 7 including a drive screw mountedon said housing in engagement with said wedge form slit mirrors formoving said slit mirrors toward and away from said edges for varyingboth slit widths and for removing said slit mirrors from said in linebeam paths.

ll l t i

1. In a monochromator for selecting a narrow band from an incoming lightbeam, the combination of: a housing; a concave mirror mounted in saidhousing; slit means mounted in said housing defining entrance and exitslits; and a grating mounted in said housing between said slit means andsaid concave mirror, said grating having an aperture for light passagebetween said slits and concave mirror; said slit means including spaceDfirst and second edges and first and second slit mirrors, with saidfirst edge and slit mirror defining said entrance slit and with saidsecond edge and slit mirror defining said exit slit, and means forpositioning said first slit mirror for reflecting an incoming beam fromsaid entrance slit to said concave mirror through said grating aperture,with said concave mirror reflecting the beam from said first slit mirroras a collimated beam to said grating and reflecting a return collimatedbeam from said grating to said second slit mirror through said gratingaperture, and means for positioning said second slit mirror forreflecting the beam from said concave mirror through said exit slit,with said concave mirror including means defining a nonreflecting zoneat the center thereof for preventing direct reflection from saidentrance slit to said concave mirror and back to said exit slit.
 2. Amonochromator as defined in claim 1 including: a frame for holding saidgrating; pivot means for mounting said frame in said housing forpivoting about an axis parallel to said slits; and drive means carriedby said housing for moving said grating on said axis.
 3. A monochromatoras defined in claim 2 wherein said drive means includes: mating threadednut and shaft mounted on said housing, with rotation of said nut movingsaid shaft; a first rod sliding in a first passage in said housing withone end of said rod engageable with said frame and with the other endengageable with said shaft; a second rod sliding in a second passage insaid housing with one end of said rod engageable with said frame; and aspring in said second passage and urging said second rod into engagementwith said frame urging said frame into engagement with said first rodurging said first rod into engagement with said shaft.
 4. Amonochromator as defined in claim 2 wherein said drive means includes:first and second rings threadedly mounted on said housing, with saidrings engageable with each other for locking on said housing anddefining a zone between said rings; a shaft carried on said frame andprojecting into said zone; and a spring carried on said housing andcoupled to said shaft urging said shaft into engagement with one of saidrings.
 5. A monochromator as defined in claim 1 wherein said gratingaperture is formed by a hole through the grating.
 6. A monochromator asdefined in claim 1 wherein said grating aperture is formed by twoindividual gratings spaced from each other with the aperturetherebetween.
 7. A monochromator as defined in claim 1 wherein saidfirst and second edges are parallel and said first and second mirrorsare mounted in a wedge form with the apex of said wedge positionablebetween said edges defining said first and second slits, with the beampath to said entrance slit in line with the beam path from said exitslit.
 8. A monochromator as defined in claim 7 including a drive screwmounted on said housing in engagement with said wedge form slit mirrorsfor moving said slit mirrors toward and away from said edges for varyingboth slit widths and for removing said slit mirrors from said in linebeam paths.